By compiling a broad photometric coverage, the rest-frame luminosity at 2500 Å can be computed via interpolation for the majority of the QSOs whenever the reference frequency is covered by the SED. Otherwise, the value can be extrapolated by considering the slope between the luminosity values at the closest frequencies, for instance.
To obtain the rest frame luminosities at 2 keV, a detailed X-ray spectral analysis of large samples of QSOs is, again, impractical. Therefore, to compute the rest-frame 2 keV monochromatic flux, a photometric approach is a viable solution for large number of sources. Briefly, the rest-frame 2 keV flux densities and the relative (photometric) photon indices, \(\Gamma _X\)  (along with their 1\(\sigma \)  uncertainties), can be derived from the 0.5–2 keV (soft) and the 2–10 keV (hard) fluxes which are tabulated in many online X-ray catalogues (i.e. XMM-Newtonhttp://xmmssc.irap.omp.eu/Catalogue/4XMM-DR11/4XMM_DR11.html and Chandrahttps://cxc.cfa.harvard.edu/csc/). The interested reader should refer to [1]}, [2]} for further details on the computation of these quantities.
